The boss of VTech, the children’s connected toy maker who suffered a major data breach, has admitted that he does not yet what the full cost of it will be.

Speaking to the Wall Street Journal, chief executive Allan Wong said: "Certainly there is financial impact to us in this whole incident by not having the service online before Christmas, but our top priority is on getting the data secured".

In total 6,368,509 children’s accounts were affected by the hack, including 727,155 in the UK. The firm only realised it had been breached 10 days after the event, having been contacted by a journalist.

Cyber security firm Trend Micro has reported that passwords were not saved securely enough. It says the passwords were hashed but not salted, leaving the firm vulnerable to a hash table attack.

Wong said that the firm was not yet "100% sure of the extent of the hack," but that "We know there are certain security aspects we can further improve in our system."

Data protection authorities in the UK and Hong Kong are investigating the matter, as are Attorneys general in several US states.